<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>AJAX POST</title>
    <style>
        div{
            width: 200px;
            height: 200px;
            border: 1px aqua solid;
        }
    </style>
</head>
<body>
    <div id="result"></div>
    <script>
        //获取元素对象
       const result= document.getElementById("result");
       //绑定事件
       result.addEventListener("mouseover",function(){
        //1.创建对象
        const xhr = new XMLHttpRequest();
        //2.初始化 设置类型与URL
        xhr.open('POST','http://127.0.0.1:8000/server');
        //设置请求头信息
        xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded')
        //3.发送 post设置请求参数
        xhr.send('a=100');
        //4.事件绑定
        xhr.onreadystatechange = function(){
            //判断
            if(xhr.readyState === 4){
                if(xhr.status >=200 &&xhr.status<300){
                    //处理服务器端返回结果
                    result.innerHTML =xhr.response;

                }
            }
        }
       });
    </script>
</body>
</html>